Dokugakuji, whose original name was Sha Jien, is the older half-brother of Sha Gojyo and a full-blooded youkai, born to his father's legal wife, while Gojyo was born to a human mistress. His past is marked by deep tragedy and guilt. In his youth, he attempted to protect his younger brother from their mother, who harbored a violent hatred for Gojyo. To calm her erratic and abusive behavior, he would often act as a substitute for their deceased father, a disturbing dynamic that ultimately failed. When his mother finally tried to murder Gojyo, Sha Jien killed her to save his brother's life. This act, coupled with his inability to prevent the torment Gojyo suffered, left him with profound self-loathing and a sense of failure.

Haunted by these events, he fled his former life and, approximately six years before the main story begins, stumbled into Houtou Castle. There, he was taken in without question by the young youkai prince, Kougaiji. Seeing a resemblance between the prince and his lost brother, Dokugakuji adopted his new name and swore absolute loyalty to him, vowing "I decided I owed you my all". This devotion is the core of his present identity; he serves as Kougaiji's personal bodyguard, fighting alongside him in the mission to revive the Ox-Demon Gyumaoh and opposing the Sanzo party. His relationship with Kougaiji is deeply personal. He sees the prince as a surrogate younger brother and projects his own unresolved guilt onto him, trying to atone for his past mistakes by protecting Kougaiji in a way he feels he failed to protect Gojyo. He shares a close, supportive bond with his comrade Yaone, and together they work to strengthen each other's resolve to save Kougaiji and his younger sister, Lirin.

Despite being on opposite sides of the conflict, his encounters with his biological brother, Sha Gojyo, are charged with a complex mix of rivalry and buried fraternal affection. The two brothers fight when their groups meet, yet their shared history surfaces, revealing a lingering fondness beneath their current enmity. Over the course of the story, Dokugakuji is forced to confront his own selfishness, admitting that his obsessive devotion to Kougaiji was partly a way to fulfill his own need for redemption. This self-awareness marks his personal development, as he resolves to move past his guilt and truly dedicate himself to his prince's well-being rather than his own emotional needs. In combat, Dokugakuji is a formidable fighter whose weapon of choice is a large curved sword, which he can summon at will in a manner similar to how Son Goku summons his nyoi-bo.